A signal conditioner is a device that changes or boosts the signal between the controller and the field device to make sure the communication works properly. A common application for signal conditioners is when you have a mV input from a thermocouple going into a
4 mA … 20 mA input card. A signal conditioner converts the mV signal into a 4 mA … 20 mA signal. In this blog, we will discuss 6 signal conditioners that all engineers should be aware of.
This isolator takes a pulse signal in and gives out 3 types of outputs. The first output is a repeater in the form of a passive transistor. The second output is a 4 mA … 20 mA signal with a range that you can configure via keypad or PACTware software. The third output is a dual relay that you can configure via keypad or PACTware software as well, for low/high alarms. This is an ideal isolator for a conveyor application or any other application where you must measure revolutions per minute.
As its name states, this isolator can take any type of temperature device and give out a
4 mA … 20 mA signal. This isolator needs to be configured via PACTware, where a library for the classic resistance temperature detector (RTD) and thermocouple (TC) curves are available. It also offers the option to write a temperature curve for those not-so-common temperature devices.
This is an analog input isolator that you can use to get a 4 mA … 20 mA signal from the field to the controller. What makes it so special is the flexibility it offers as far as power sources. The same unit can power a 2-wire field device or just get the 4 mA … 20 mA signal from a 4-wire field device. Alternatively, the unit can source the 4 mA … 20 mA to the controller or sink the 4 mA … 20 mA. If you’re not familiar with sourcing or sinking, you can think of this as passive or active. What is pushing the 24 V in the loop, the controller or the isolator? And finally, you can configure this isolator to give out 0 V … 5 V to the controller instead of
4 mA … 20 mA. The configuration of the unit is done via dip switches.
This isolator is a digital input device. What makes it special is the fact that it can amplify a signal and convert a NAMUR signal into a digital signal. Many sensors nowadays are NAMUR. It is important to understand that a NAMUR signal is not a digital signal because a NAMUR signal will never give you a 0 V in the loop. Because of that, a NAMUR signal cannot be connected to a digital input card. The isolator also offers single and dual outputs with relays that can handle up to 250 VAC or 40 VDC and 2 A.
What happens when an application requires the signal from one device in two different locations, let’s say local display and control room? Well, you can connect the local display in series (when possible) or you can split the signal. Splitting the signal is possible in a voltage signal, but not in a mA signal. For those applications, you can use this isolator, which takes in one 4 mA … 20 mA from a field device and give out 4 mA … 20 mA dual output.
An isolator that is quite similar to the KFD2-UT2* discussed previously. However, this device offers dual relay outputs. You can configure these relays for high/low alarm, as well as for “trent.” “Trent” is a function that activates the relay when there is a sudden change in temperature. To configure the function, it is important to define the max temperature range over time that is acceptable to change; anything over that temperature will cause the relay to activate.
And, all these great signal conditioners are also available as intrinsically safe barriers.